The XPS valence band spectra of NbC

The x-ray photoemission valence band spectra of NbC have been measured and are compared with the x-ray emission spectra and with the results from band structure calculations. This comparison leads to a large enhancement of theC2 _p photoabsorption cross section (at=1,487 eV) compared to the value calculated for the free atom. The effect of the nonmetal vacancy in the valence band can be described very well with vacancy cluster calculations.     

Theoretical study of exafs-like modulation observed in graphite 2scis spectra

The EXAFS-like oscillation observed during graphite C 2s constant-initial-state (CIS) spectroscopy using a synchrotron radiation source is analyzed within the theoretical treatment previously proposed by the authors. The interference between the electron waves emanating from different atomic sites plays an important role in the phenomenon.     

High resolution core and valence band XPS spectra of non-conductor pyroxenes

High resolution core level and valence band (VB) X-ray photoelectron spectra (XPS) of the non-conductor pyroxene minerals, bronzite ((Mg_0.8,Fe_0.2)₂Si₂O₆) and diopside (Ca(Mg_0.8Fe_0.2)Si₂O₆) have been obtained with the Kratos magnetic confinement charge compensation which minimizes differential charge broadening. Observed Si 2p, O 1s, Mg 2p and Ca 2p total linewidths are all about 1.3 eV, very similar to those observed previously with the same instrument for SiO₂ and olivines ((Mg,Fe)₂SiO₄); and we consider that these widths are within 0.05 eV of the minimum room temperature linewidths for these samples with the experimental resolution of this instrument of 0.35 eV. These linewidths are all determined by vibrational broadening due to the M-O symmetric stretch in the ion states. The Si 2p binding energies (BE) are intermediate between the quartz and olivine Si 2p binding energies; but the O 1s spectra resolve the bridging oxygen (BO) and non-bridging oxygen (NBO) in the unit, with the NBO O 1s very close in BE to the O in olivine, and the BO very close to the BO in SiO_2. Indeed in both diopside and bronzite, it is possible to separate the three structurally inequivalent O atoms in the O 1s spectra: the BO at a BE of about 532.6 eV, a NBO peak from the MgOSi moiety (Mg in the M1 site) at about 531.3 eV, and a NBO peak at 531 eV from the CaOSi or the FeOSi moieties (Ca and Fe in the M2 site). The O 1s BE increases with the increase in the electronegativity Ca < Mg < Fe < Si. Moreover, the linewidths of these peaks increase when Fe and Mg are both present in either M1 (diopside) or M2 (bronzite) sites.The valence band spectra for the two pyroxenes are rather similar, and quite different from the VB spectra of quartz and olivines. The dispersion of the pyroxene VB spectra is intermediate between the VB spectra of quartz and olivines; the valence band spectrum of pyroxenes are more dispersed than in olivines by about 1.5 eV but less dispersed than quartz by about 1.5 eV. These VB spectra can be assigned using the previous olivine VB spectra and high quality pseudopotential density functional theoretical calculations in the generalized gradient (GGA) approximation. As for the olivine VB spectra, the Fe 3d t_2g and e_g orbitals in M1 and M2 sites of the pyroxene are located at the top of the pyroxene valence band, and the BE of the Fe 3d peaks from M1 are about 0.7 eV smaller than the Fe 3d peaks in M2. The theoretical XPS valence band spectra using the theoretical density of states and the Gelius intensity approximation are is in good semi-quantitative agreement with the experimental spectra. This intermediate dispersion of pyroxenes is due to the partial polymerization of the Si-O units in pyroxenes, and the intermediate charge on the Si atoms as indicated by the Si 2p BE.     

RPA-boson approach to many-body effects observed in the high-energy XPS spectra

Intensities of shake-up satellites and relaxation energy accompanied by deep core ionization are calculated within RPA-boson approximation. The relaxation energy is closely related to the intensities of shake-up and -off satellites in this theoretical framework.     

XPS valence band spectra of Nb3Sn,Nb and Sn

XPS valence band spectra of Nb₃Sn, Nb and Sn have been obtained under high resolution. The 4d band structure in the Nb₃Sn spectrum is similar to that seen in Nb metal.     

An XPS study of the valence bands in solid and liquid bismuth

High resolution XPS measurements on bismuth show the valence band structure of the liquid phase to be very similar to that of the solid and very different from that of free electrons. The spectra are in general accord with recent calculations of the densities of states for crystalline and amorphous group V elements.     

XPS study of the valence band spectrum of amorphous Fe-B alloys

XPS spectra of Fe 3s and Fe 3p levels and Fe 3d valence band of amorphous iron-boron alloys were measured as a function of boron concentration over the range from 12 to 25 at% B. It was found that a characteristic hump appeared at lower energy region in Fe 3d band spectrum of every amorphous Fe-B alloy. The origin of the hump was discussed in terms of the formation of a new bonding state between Fe and B atoms in amorphous Fe-B alloys.     

The XPS valence band of nickel metal

The XPS valence band spectrum of evaporated nickel is compared with a theoretical density of states curve and with a synthetic density of states curve obtained by adding two XPS valence band spectra of copper shifted by 0.3eV with respect to each other. Both calculated curves agree with the main features of the XPS valence band spectrum.     

Ab initio study of valence correlation satellites in photoelectron spectra of neon

Ab initio calculations of energies and widths of the valence correlation satellites in the binding energy region between 48 and 99 eV of the photoelectron spectrum of neon are presented. The results are compared with the high-resolution, synchrotron radiation excited valence photoelectron spectra recorded by Kikas et al. [J. Electron Spectrosc. Relat. Phenom. 77 (1996) 241] using photon energies of 96 and 169 eV and with previous synchrotron radiation and conventional radiation studies. Our calculations allow a deeper insight in the regions where a bunch of states, different in spin and angular momentum, are concentrated, and add considerable information on assignment and width of several transitions. The theoretical spectrum calculated in the region between 74 and 94 eV compares quite well with the experimental one.     

Incommensurate valence modulation in high-Tc cuprates

An incommensurate modulation has been observed in a Cu-rich La2CuO4.003 crystal. It is shown that the modulation results from a periodically distributed holes lying on the CuO2 planes, and that the hole modulation may be regarded to be a kind of valence modulation. It is shown that appreciable valence modulation contrast may be generated by the mechanisms of hole scattering alone when the period of the modulation is of the order of 2 nm.     

Theoretical study of X-ray photoelectron spectrum of germanium valence electrons

The density of states and X-ray photoelectron spectra of germanium valence electrons have been calculated. It is shown that to describe the shape of the photoelectron energy distribution curve of the greatest importance is precise allowance for the particularities of energy band structure and the ratio between excitation probabilities of s- and p-electrons. This is possible if the valence electron states are described with a linear combination of atomic orbitals while the excited electron states are described with the orthogonalized plane wave.     

Surface effects in the valence band XPS spectrum of copper

Comparison of valence band XPS spectra of Cu samples with theoretical density of states shows a high intensity near the upper edge of the d-band. This is a feature common for most d-band metals. However, if the difference in the density of states of the first two atomic layers with respect to the bulk is taken into account, good agreement between theory and experiment is found.     

Theoretical study of phonon spectra in ferromagnetic nanoparticles

Based on the spin-phonon model we analyze the influence of surface and size effects on the phonon properties of ferromagnetic nanoparticles. A Green's function technique in real space enables us to calculate the renormalized phonon energy and its damping depending on the temperature and the anharmonic spin-phonon interaction constants. With decreasing particle size the phonon energy can decrease or increase for different surface spin-phonon interaction constants, whereas the damping increases always. The influence of an external magnetic field is discussed, too. The theoretical results are in reasonable accordance to experimental data.     

Comparison of the background corrected valence band XPS spectra of Fe and Co aluminides and silicides with their electronic structures

The background corrected valence band XPS spectra and the electronic structures of FeAl, FeSi, CoAl and CoSi were studied. Clean surfaces of the polycrystalline samples were obtained by in situ fracturing of the samples in an XPS spectrometer. The energy loss parts of the Fe 2p, Co 2p and valence band spectra were removed by the deconvolution method using Al 2s or Si 2s spectra as response functions. CoAl exhibited a satellite peak in the Co 2p region, but the other compounds had no clear satellite peaks in the Co 2p and Fe 2p regions. The experimentally background corrected valence band spectra were compared with the calculated spectra using the first-principle band calculation. There were large discrepancies between the spectra above the binding energy of 5 eV. These indicated that the experimental spectra could not be explained by the electronic structures of the ground states alone.     

Multielectron effects in the XPS spectra of nickel

Extra structure in the XPS spectra of Ni metal is interpreted as arising from a localized d-hole accompanying the hole state created by the photoemission process. This d-hole state has a binding energy of approximately 6 eV.     

On calculating intensity from XPS spectra

The intensity calculation is the basis for all quantitative applications of electron spectroscopy. Unfortunately, some misinterpreted terms are used and correctly interpreted terms are misused in the overwhelming majority of publications in XPS, including most textbooks as well as accepted and proposed standards. Due to this mistake the number of the detected electrons is given as having dimension of energy (?) and also the formulas for calculating the peak area and its standard deviation are wrong. Since in all other spectroscopic fields the number of the detected particles is dimensionless, continuing this practice leads to isolating XPS from both other measurement sciences and theory, because the measured total intensity in XPS is simply not comparable to the ones derived with other spectroscopic methods or theoretically. Therefore, the basic measuring processes and terms are critically reviewed and their physically correct interpretation is given. This interpretation reveals that the error is hidden in the incorrect interpretation of both the measurement process and the measured quantity. It is shown that through using the correct interpretation both the dimensions of the intensity calculated from electron spectroscopic measurements as well as the formulas related to the intensity and its standard deviation will agree with all other spectroscopic fields.